Steam separating means for boiling water reactors

ABSTRACT

A boiling water reactor which comprises a reactor tank and a moderator tank located inside the reactor tank has a lid with a plurality of upstanding pipes opening into steam separators. The steam separators are secured together in groups, and each group is clamped to the lid. Each steam separator has a rising tube and each unit has a bell-shaped casing common to the group and surrounding the steam separators to provide a falling surface for the water separated in the unit. Deflection caps connected together in groups corresponding to the groups of steam separators are mounted above the open tops of the steam outlet tubes of the separators.

States Patent [191 Mansson et al.

[111 3,,07 June 28, 1974 1 STEAM SEPARATING MEANS FOR BOILING WATER REACTORS 3,066,088 11/1962 Blaser 176/54 X 3,185,630 5/1965 Ammon 176/54 3,253,999 5/1966 Weisman 176/55 3,342,690 9/1967 Stern:: 176/54 3,625,819 12/1971 Sodergard 176/54 FOREIGN PATENTS OR APPUCATIONS 1,082,992 6/1960 Germany 176/54 Primary Examiner-Carl D. Quarforth Assistant Examiner-E. E. Lehmann [5 7] ABSTRACT A boiling water reactor which comprises a reactor tank and a moderator tank located inside the reactor tank has a lid with a plurality of upstanding pipes opening into steam separators. The steam separators are secured together in groups, and each group is clamped to the lid. Each steam separator has a rising tube and each unit has a bell-shaped casing common to the group and surrounding the steam separators to provide a falling surface for the water separated in the unit. Deflection caps connected together in groups corresponding to the groups of steam separators are mounted above the open tops of the steam outlet tubes of the separators.

8 Claims, 7 Drawing Figures 1 Ir /3 LI PM EWED W4 SHEET 2 OF 6 INVENIUR. v

PATENTEDJUHZB m4 SHEET 5 OF 6 Fig. 6

IN VENT 0R.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam separating arrangement for a boiling water reactor.

2. The Prior Art Swedish Pat. No. 324,189 describes a boiling water reactor having internal steam separation. In this reactor, the steam-water mixture produced in the core is led up through the moderator tank lid to a steam-treating unit in which the steam is de-moisturized in two steps, first in steam separators which separate most of the water from the steam, and then in a steam dryer which removes the remaining water so that the steam emerging from the reactor is saturated but not essentially moist. The steam separators are situated one beside the other and are of the centrifugal type. Each separator has a vertical rising tube .which is welded to the lid of the moderator tank and has a ring of oblique guide vanes to cause the steam-water mixture to rotate so that the water is forced out towards the tube wall while the steam collects along the tube shaft and can be removed at the top through a steam outlet tube concentric with the rising tube. The separated water turns and falls down inside an outer falling tube which is concentric with said tubes. Still more water can be separated in the steam separator by means of a deflection cap welded to the steam outlet tube and located above its outlet, before the steam passes on to the steam drying stage.

SUMMARY OF THE INVENTION In this known reactor .there are considerable difiiculties connected with inspecting and possibly replacing one or more of the steam separators when the reactor is shut down for fuel exchange. If a replacement is necessary, a complete steam-separator-moderator-tank-lid unit must be exchanged. The lack of space makes it difficult to make the falling tubes sufficiently wide. These drawbacks are eliminated by giving the reactor according to the invention the form of a reactor tank and a moderator tank located inside the reactor tank with a lid with a plurality of up-standing pipes opening into steam separators. The steam separators are secured together in groups, and each group is clamped to the lid. Each steam separator has a rising tube and each unit has a bell-shaped casing common to the group and surrounding the steam separators to provide a falling surface for the water separated in the unit. Deflection caps connected together in groups corresponding to the groups of steam separators are mounted above the open tops of the steam outlet tubes of the separators.

Such a reactor gives considerably improved servicing 7 possibilities and thus, indirectly, economic gains. Furthermore, the falling area for the water can easily be made sufficiently large.

BRIEF DESCRIPTION OF THE DRAWINGS section Il--II in FIG. 1. FIG. 3 shows a longitudinal section of a steam separator unit in the reactor. FIGS. 4 and 5 show cross-sections lV-IV and V-V, respectively in FIG. 3. FIG. 6 shows the upper end of a connecting rod in the unit and FIG. 7 its lower end.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The boiling water reactor shown in FIGS. 1 and 2 has a reactor tank 1 and a moderator tank 2 located therein. The moderator tank 2 surrounds the reactor core 3 which is built up of a plurality of parallel, vertical fuel assemblies 4, only two of which are shown. The active part of the core, i.e., the part containing the nuclear fuel, is indicated by a dotted line. The fuel assemblies 4 are supported at the top by a core grid 5 resting on a ledge 6 in the upper part of the moderator tank 2. The moderator tank 2 has a lid means 7 consisting of an arched moderator tank lid 8 having a plurality of passages 9 through the lid to allow the steam-water mixture produced in the core to pass upwardly, and a pipe stub 10 projecting upwardly from the lid, attached in each passage 9. The stubs 10 have slightly different lengths so that their upper ends all lie in a single horizontal plane. The lid 8 is attached to the moderator tank 2 by means of a hook joint, not shown.

From each pipe stub 10, the steam-water mixture is led into a steam separator 11 of centrifugal type. The steam separators 11 are located one beside the other and are collected in groups to form units 12 which are held clamped against the pipe stubs 10 by means of clamping devices 13. As can be seen in FIG. 2, the steam separators 11 are arranged in a hexagonal lattice and most of the units 12 comprise seven steam separators, one central and sixsurrounding ones, whereas some of the outer units 12 comprise only five steam separators, in order to best utilize the circular space in the cross-section above the moderator tank. Of course the steam separators may also be arranged in a square lattice, in which case at least most of the units comprise four or nine steam separators, but. a hexagonal lattice makes it easier to pack the steam separators tightly. It is also possible to build up a hexagonal lattice of five separator units.

From FIG. 3, which shows the unit 12, it is clear that the steam separators 11 are constructed in a substantially conventional manner for centrifugal separators. Each steam separator 11 consists of a riser pipe 14 which at the top has a perforated, conically narrowing part 15, a guide rail ring 16 attached to the lower part of the riser pipe and having a hub 17 and oblique blades 18 to bring the steam-water mixture to rotate vigorously so that the water is thrown out against the wall of the riser pipe 14 and the steam is pressed in towards the longitudinal axis of the riser pipe. It also consists of a steam outlet tube 19, concentric with the riser pipe 14 projecting into the upper end of the riser pipe to slightly below the start of its perforated, conically narrowing part 15. The steam tube 19 has a lower, conically narrowing inlet 20 and an upper, conically expanding outlet 21.

In conventional steam separators, the upper part of the riser pipe 14 and the steam tube 19 is surrounded by a falling surface concentric therewith, in which the separated water which is pressed out through the perforated conical part 15 alters direction and falls down into an annular gap located between the riser pipe and the falling surface, to be then circulated again through the core. In the unit according to FIG. 3 the falling surface has been replaced by a bell-shaped casing 22, common for the group of steam separators, which has a vertical wall 23 and a horizontal roof 24. The casing surrounds the steam separators at the top, but the outlet 21 of the steam tube 19 projects through the roof 24 and is welded to this roof. The wall 23 of the casing is corrugated and fits the shape of the riser pipe 14 in the unit 12 so that the falling area for the water can easily be made sufficiently great since here the substantially triangular cross-sectional area is also used which in conventional constructions is situated between three adjacent falling tubes. An upper support grid 25 joins the central steam tube 19 in the group with the six surrounding tubes and, as shown in FIG. 4, the six sur' rounding tubes with the wall 23 of the casing at two points each. A central support grid 26 joins the central riser tube 14 to the six surrounding ones (see FIG. and a lower support grid 27 joins the outer riser rubes 14 at two points each to the casing wall 23. In this way the unit 12 will be very strong and resistant to vibratrons.

Above each steam outlet 21 is a domed deflection cap 28 to separate still more water. The six outer caps 28 are held together by cross-pieces 29 to form a hexagonal ring, and from the central cap 28 there are three spokes 30, the outer ends of which are attached to the middle of one of the cross-pieces 29 each, as shown in FIG. 2. A lifting eye 31 is attached to the starting point of the spokes above the central cap 28 and each spoke 30 is screwed by means of a nut 32 to a peg 33 projecting from the roof 24 of the casing. The pegs 33 are of such a length that the deflection caps 28 are positioned a suitable distance above the steam outlets 21 and the attachment of their ends in the roof 24 of the casing is reinforced by oblique strips of metal 34. This is seen most clearly in FIG. 6. The lifting eye 31, spokes 30 and pegs 33 are sufficiently strong to permit the entire steam separator unit 12 to be lifted by the lifting eye 31. When the three nuts 32 have been unscrewed all seven deflection caps 28 can be removed as a unit so that the steam separators can be inspected internally with ease, for example with the help of an endoscope.

As mentioned above, the steam separatorunit 12 is held clamped against the lid means 7 by clamping devices 13. This clamping device comprises an elongate, vertical connecting rod 35, shown in its entirety in FIG. 3, and the upper and lower ends of which are shown on a larger scale in FIGS. 6 and 7, respectively. The connecting rod 35 is manufactured of high quality material and has a long central part which is considerably narrower than its end parts so that, due to predetermined stretching of the rod, it is easier to achieve welladjusted clamping of the unit 12. The narrow central part must be protected against vibrations and the connecting rod 35 is therefore surrounded by a supporting protective tube 36 having guides 37 for the rod. The lower end part of the connecting rod 35 fits accurately in the protective tube 36 and its lowest part is shaped as a screw 38 with hexagonal head 39. The protective tube 36 has an internal hexagon fitting thishead and an external hexagon 40 offering a grip for a spanner. The connecting rod is screwed to a connecting rod attachment 41 with a lower part 42 which is welded to connection pieces on the lid of the moderator tank and has its upper surface on a level with the upper surface of the connection pieces, and an upper transition part 43 welded thereto of an exact length and provided with a threaded hole 44 for the screw 38 of the connecting rod. The transition part 43 is provided on the outside with two diametrically opposite parallel grooves 45 into which the lower edge of the protective tube 36 is pressed to lock the screw joint. The locking is not so strong that the lower edge of the protective tube is not automatically pressed out of the groove 45 when the connecting rod is loosened with a spanner gripping the external hexagon 40 on the protective tube. The protective tube and connecting rod can only be attached or loosened when the steam separator unit 12 is not in position. They are therefore not a part of the unit.

In order to clamp a seven-separator unit, three connecting rods are used, while a five-separator unit is claimed with two, and a three or four separator unit could be clamped with only one connecting rod. In order that, when the unit 12 is lowered towards the lid means 7, it will be guided into exactly the right position in relation to the three free connecting rods 35 with the protective tubes 36, there are three short guide tubes 46 attached to the lower side of the roof 24, these tubes being funnel-shaped (FIG. 3), as well as two guide vane rings 16 at the lower periphery provided with guide rings 47 of such inner diameter that they can engage against the outside of the connection pieces 10. When the unit 12 is in position, the connecting rod 35 and protective tube 36 project up through the roof 24 of the casing. The protective tube 36 ends approximately on a level with the deflection caps 28 and are surrounded by a stable upper tube 48 welded to the upper side of the roof 24 and ending at the top in a strong flange 49. The central hole of the flange becomes narrower towards the top and provides a guide for the upper end part of the connecting rod which, above the flange, is shaped with a thread 50, a narrower hexagonal part 51, a neck 52 and uppermost a head 53, this also being narrower than the threaded part. In this way a clamping nut 54 engaging in the thread 50 can be completely removed from the connecting rod 35 when the unit 12 is to be detached from the lid means 7. The clamping nut 54 has a downwardly directedly, tubular projection 55, the lower edge of which is intended to abut the upper side of the flange 49.

When the unit 12 is to be clamped, a device is used which, while being supported against the upper side of the flange 49, grips the head 53 and stretches the connecting rod to a predetermined pre-stressing, after which the clamping nut 54 is screwed to abutment against the flange 49. The prestressing device grips the hexagonal part 51 of the connecting rod and thus prevents the narrow central part of the rod from being subjected to twisting stresses. The unit is unclamped in a corresponding manner.

We claim:

1. Boiling water reactor comprising a reactor tank (l), a moderator tank (2) located inside the reactor water mixture produced in the core to the steam separators to separate most of the water from the steam, in which the steam separators (11) are secured together in groups to form units (12), and clamping devices (13) for clamping each of said groups to the lid means, the passages (9) comprising pipe stubs (10) projecting upwardly from the lid (8) of the moderator tank and each steam separator (11) having a rising tube (14), and each unit (12) comprising a bell-shaped casing (22) common for the group and surrounding the steam separators (11) at the top, the casing being rigidly joined to the rising tube (14), and the clamping device (13) comprising at least one slim, vertical connecting rod (35), a connecting rod attachment (41) for attaching the lower end of the connecting rod to the lid means (7), the upper end of the connecting rod being provided with members (54) for at least indirectly pressing the casing (22) downwardly and thus pressing the rising tube (14) against the pipe stubs (10).

2. Boiling water reactor according to claim 1, in which the connecting rod (35) isvprovided at the top with a thread (50) and a nut (54) running in said thread, which nut at least indirectly abuts against the casing (22), the connecting rod (35) above the nut (54) being providedwith a head (53) which offers an attachment point for a tension member, whereby, by stretching the connecting rod (35) in relation to the casing (22) to a certain value before screwing in the nut (54) to abutment, a pre-determined pre-stressing will be obtained in the connecting rod (35).

3. Boiling water reactor according to claim 2, in

which the connecting rod (35) has a long central part which is narrower than its end parts.

4. Boiling water reactor according to claim 3, in which above the thread (50) the connecting rod 35 is provided with means operable upon engagement of the gripping member to prevent the rod (35) from being twisted when the nut (54) is screwed in or out.

5. Boiling water reactor according to claim 3, in which the connecting rod (35) is passed through the casing (22) inside a supporting protective tube (36) with guides (37) for the rod.

6. Boiling water reactor according to claim 1, in which the wall of the casing (22) provides a falling surface for the water separated in the unit (121).

7. Boiling water reactor according to claim 6, in which the wall of the casing (22) is corrugated to fit the contour of the rising tube (14) in the unit (12).

8. Boiling water reactor according to claim 1, in which each steam separator (11) is of centrifugal type and has a steam outlet tube (19) projecting through the top of the casing (22) and a deflection cap (28) located above the steam outlet tube, and in which the deflection caps (28) associated with the unit (12) are mutually connected and detachably connected to the rest of the unit (12). 

1. Boiling water reactor comprising a reactor tank (1), a moderator tank (2) located inside the reactor tank and having a lid means (7), a plurality of steam separators (11) located one beside the other above the lid means, and a core (3) located inside the moderator tank, the lid means comprising a lid (8) for the moderator tank having passages (9) therethrough communicating with the steam separators to lead the steam-water mixture produced in the core to the steam separators to separate most of the water from the steam, in which the steam separators (11) are secured together in groups to form units (12), and clamping devices (13) for clamping each of said groups to the lid means, the passages (9) comprising pipe stubs (10) projecting upwardly from the lid (8) of the moderator tank and each steam separator (11) having a rising tube (14), and each unit (12) comprising a bell-shaped casing (22) common for the group and surrounding the steam separators (11) at the top, the casing being rigidly joined to the rising tube (14), and the clamping device (13) comprising at least one slim, vertical connecting rod (35), a connecting rod attachment (41) for attaching the lower end of the connecting rod to the lid means (7), the upper end of the connecting rod being provided with members (54) for at least indirectly pressing the casing (22) downwardly and thus pressing the rising tube (14) against the pipe stubs (10).
 2. Boiling water reactor according to claim 1, in which the connecting rod (35) is provided at the top with a thread (50) and a nut (54) running in said thread, which nut at least indirectly abuts against the casing (22), the connecting rod (35) above the nut (54) being provided with a head (53) which offers an attachment point for a tension member, whereby, by stretching the connecting rod (35) in relation to the casing (22) to a certain value before screwing in the nut (54) to abutment, a pre-determined pre-stressing will be obtained in the connecting rod (35).
 3. Boiling water reactor according to claim 2, in which the connecting rod (35) has a long central part which is narrower than its end parts.
 4. Boiling water reactor according to claim 3, in which above the thread (50) the connecting rod (35) is provided with means operable upon engagement of the gripping member to prevent the rod (35) from being twisted when the nut (54) is screwed in or out.
 5. Boiling water reactor according to claim 3, in which the connecting rod (35) is passed through the casing (22) inside a supporting protective tube (36) with guides (37) for the rod.
 6. Boiling water reactor according to claim 1, in which the wall of the casing (22) provides a falling surface for the water separated in the unit (12).
 7. Boiling water reactor according to claim 6, in which the wall of the casing (22) is corrugated to fit the contour of the rising tube (14) in the unit (12).
 8. Boiling water reactor according to claim 1, in which each steam separator (11) is of centrifugal type and has a steam outlet tube (19) projecting through the top of the casing (22) and a deflection cap (28) located above the steam outlet tube, and in which the deflection caps (28) associated with the unit (12) are mutually connected and detachably connected to the rest of the unit (12). 